Hi. I have both versions 8 and 9, but don't like 9 and so do everything in 8, so forgive me if this advice is inapplicable to you. I cannot say why your transparent png isn't working... however I can give you a workaround.

From the preview window select the image.
From Visual Properties find the check box for choosing particular colours to treated as transparent.
There's an eye drop option to allow you to select the precise colour you want to ignore.

Then perhaps the thing to do might be to fill the transparency with Snagit (love that program) with, say, purple, and preserve the main image - then in Camtasia eliminate the purple. You shouldn't have to go through this pain, I know. But if you are in a hurry and no one else can offer a better solution, this would work.

Another thing to check is to use the image elsewhere. Perhaps even in SnagIt. Drag it on top of another image and see if it's truly "transparent". I've had it happen more than once where I thought I saved an image with a transparent background but for whatever reason, it just refused to save that way. In some cases I had to resort to just creating a totally new blank image. Then copy the one giving me fits and paste into the new image. Then saving the new image.

You can, normally the canvas is automatically set to Transparent when you open a open a png in SnagIt.Why this isn't working for you is a bit of a mystery. Most versions of SnagIt don"t have settings that let you set a default canvas color. I think SnagIt 12 was the only version that allowed it?Maybe a computer or SnagIt restart will change things?A Repair or Re-Install of SnagIt . You didn't mention what version you are running.